Todays high performance aircraft more than at any time in history are placing exacting demands on the fuel pumps that provide a controlled supply of fuel to be burned in the engines. In the prior art one finds typically, engine driven gear pumps sized for maximum output at sea level. These pumps are hydraulically connected in combination with fuel pump by-pass valves and lines as well as a metering valve controlled by a hydromechanical computer. The computer is responsive to such inputs from the engine as speed as well as various pressures and temperatures. A pilot's power control lever is coupled to the computer and pilot controlled position of the control lever dictates the power sought from the engines. The metering valve is controlled by the hydromechanical computer to provide a variable area for fuel to pass on its way to be burned in the engine or engines.
The aircraft of the future that are in the process of being manufactured and are on the drawing boards today, have available a most powerful tool in the form of the microprocessor technology. A microprocessor loaded computer can and will handle more efficiently all the functions of the prior art by-pass valves, lines, hydromechanical computer and metering valve, all in such a manner that a single control signal will be provided that will establish by closed loop control on the engine process the fuel flow required for a specific level of power commanded by the pilot. Ideally this single signal would be coupled to a servo which servo would in turn directly control an infinitely variable fuel pump. The centrifugal pump to be described in detail hereinafter meets the needs of the future by providing a pump with a modulatable output that can be varied infinitely, that can withstand the ever present hostile problem created by the presence of unfiltered contaminant particles inherently present in fuel and fuel delivering systems and will minimize the temperature rise of the fuel flowing through it and thereby maximizing the fuel heat sink available for cooling the air frame and engine systems.
Variable diffuser centrifugal pumps for minimizing pump fluid temperature rise by reducing recirculation losses are not new as is evidenced by U.S. Pat. No. 3,784,318 to Donald Y. Davis. The Davis pump is provided with a discharge shutter valve which provides a variable diffuser for the pump. The shutter valve 52, best seen in FIG. 4, includes a hollow slotted cylinder positioned for movement into a variety of operative positions between an impeller 14 and diffuser vane passages 26. The Davis invention does not provide for, as the invention being described hereinafter, a pump having infinitely variable single or independently modulatable multiple pump outputs capable of handling a fluid containing solid contaminant particles.
A typical fluid delivering system of the prior art as noted earlier which includes a shuttered diffuser, a centrifugal pump operating at a fixed speed ratio to the engine, a metering valve for distributing fluid delivered by the pump and a control system for positioning the shutter in response to the operation of the metering valve is set forth in U.S. Pat. No. 3,826,586 to Richards. The specification of Richards indicates that the combination just recited is a typical environment where a shutter diffuser valve of the type shown by Davis would find utility. The Richards patent fairly represents the prior art and represents to the extent shown a technological benchmark from which the invention to be described hereinafter provides a fresh and new departure in providing a pump that has single or multiple outputs which are independently infinitely variable. The pump containing the invention is also capable of effectively dealing with contaminant particles carried by the fluid.
A patent worthy of inclusion in the background art from which the subject invention advances the state of the art is found in the U.S. Pat. to S. O. Johnson, No. 2,991,982 and E. L. Small, No. 114,211. Both of these patents deal with fluid handling systems and illustrate simultaneous uniform movement of a number of elements to control fluid flow. The Johnson patent is directed to a centrifugal fluid moving device while the Small patent is directed to an improvement in a water wheel. Neither of these patents consider the problem of contaminant particles in the fluid becoming lodged in the moveable elements, nor do these patents provide for contaminant particle handling as will become evident in the description that follows in respect of the invention hereinafter described.